1. Field of Invention
The present invention relates to a method for making a solar cell and, more particularly, to a method including the steps of coating various layers of a solar cell on different substrates and joining together the laminates, thus making the solar cell efficiently.
2. Related Prior Art
As the population of the world is growing, the consumption of energy is increasing while the reserve of fossil fuel including gasoline, natural gas and coal is declining. Moreover, the environmental pollution is getting worse. Hence, many efforts are made to use renewable energy. To use various types of the renewable energy, there are various types of devices such as fuel cells, solar cells, wind turbines and damps. Compared with a power plant based on wind turbines or a damp, the cost for constructing a power plant based on solar cells is low and the area of the power plant based on the solar cells is small. Hence, solar energy seems the most promising type of the renewable energy.
Generally, the operation of the solar cells is based on semiconductor materials that generate electricity after they absorb sun light. Based on materials and techniques, the solar cells can be classified as chip-type solar cells and thin-film solar cells. A chip-type solar cell includes a p-type semiconductor silicon chip that goes through superficial etching, p-n junction diffusion, anti-reflection film coating and electrode making by screen printing. There is however a serious problem with the use of a chip-type solar cell. The amount of the electricity generated by a chip-type solar cell is less than the amount of electricity consumed to make it.
On the other hand, a thin-film solar cell includes various films made of various materials that generate electricity after they absorb sun light. For example, referring to FIG. 1, a thin-film solar cell 9 includes various films formed on a substrate 90. To make the solar cell 9, a Mo metal layer 91 is formed on the substrate 90 before an absorbing layer 92 is formed on the Mo metal layer 91. A CdS layer 93 is formed on the absorbing layer 92 before an intrinsic ZnO (“i-ZnO) layer 94 is coated on the CdS layer 93. Then, a ZnO:Al (“AZO”) layer 95 is formed on the i-ZnO layer 94. Finally, an anti-reflection layer 96 and an external electrode 97 are formed on the AZO layer 95.
Generally, the substrate 90 can be made of soda-lime glass. The absorbing layer 92 is made of a p-type semiconductor material such as CIS or CIGS. The AZO layer 95 can be made of an n-type semiconductor material. That is, the structure of the solar cell is a structure based on a p-n junction. The CdS layer 93 can be called the “buffering layer” to increase the absorption efficiency. Moreover, because a semiconductor surface is reflective, all of the sun light does not enter the solar cell 9. That is, there is loss of sun light. Hence, the anti-reflection layer 96 can be made of MgF2 for example to increase the proportion of the sun light that enters the solar cell 9.
The present invention is therefore intended to obviate or at least alleviate the problems encountered in prior art.